Cyclooxygenase-2 selective inhibitors constitute an important class of non-steroidal anti-inflammatory drug substances (NSAIDs), especially due to their improved safety profile. Commonly used NSAIDs, for example aryl propionic acid or aryl acetic acid derivatives are known to cause gastric irritation and ulceration upon prolonged use of such drugs. Cyclooxygenase-2 inhibitors, which act on mechanism of isozyme expression in inflamed tissues, show better safety in this regard.
Etoricoxib selectively inhibits isoform 2 of cyclooxygenase enzyme (COX-2) and currently it is approved in more than 70 countries for therapeutic indications like treatment of rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, chronic low back pain, acute pain, osteoarthritis and gout.
Compounds of general formula (A) including Etoricoxib are disclosed in U.S. Pat. No. 5,861,419 as depicted in the following scheme.

An alternate process is also disclosed in U.S. Pat. No. 5,861,419 as depicted in the following scheme.

The processes described in U.S. Pat. No. 5,861,419 comprise multi-step synthesis resulting in poor yield of the final product.
U.S. Pat. No. 6,040,319 describes another process for the preparation of Etoricoxib according to the scheme below. It relates to condensation between a compound of Formula-II and a compound of Formula-IIIa, wherein X may be selected from phosphates, sulfates, acetates, perchlorate, borates, benzoate, napsylate, particularly, hexafluorophosphate, sulfate, mesylate, tosylate, triflate, acetate, trifluoroacetate, tetrafluoroborate, tetraphenyl borate, hexafluoroantimonate, chloride, bromide, fluoride, iodide, benzolate and napsylate. Sodium or potassium hydroxides, cesium carbonate, alkoxides, amides and hydrides of lithium, sodium and potassium depicted as suitable bases.

WO 99/55830 describes a process for preparing cox-2 inhibitors including etoricoxib. It involves condensation between a vinamidinium salt and a substituted benzyl pyridyl ketone derivative, which in turn is made by employing a Grignard reaction between a pyridyl amide derivative and a thiomethyl benzyl halide, followed by oxidation.
U.S. Pat. No. 6,071,936 includes substituted pyridine derivatives, their pharmaceutical compositions and a method of treating cox-2 mediated diseases. Various compounds included therein are structurally 2,3-diarylpyridine derivatives having a sulphone substitution. The synthetic scheme comprised of a palladium catalyzed diaryl coupling between a halogenated 2-aminopyridine derivative and a 4-(methylthio)phenylboronic acid followed by oxidation and further coupling with another aryl moiety.
U.S. Pat. No. 6,001,843, U.S. Pat. No. 6,596,736 B2 and U.S. Pat. No. 6,812,346 B2 also discloses structurally similar substituted pyridine derivatives and synthetic methodology applied. Their use in preparation of pharmaceutical formulations as cox-2 inhibitors is also presented in these inventions.
The patent document WO2010/097802 A2 describes a process for preparing the drug substance etoricoxib. While use of certain substituted β-chloro vinamidinium salts has been reported earlier, this invention relates to preparation of alternative β-chloro vinamidinium salts containing a cyclic or a heterocyclic substitute group. It also describes a process for preparing these alternative vinamidinium salts, as well method of purification. Polymorphic characteristics of one of such modified β-chloro vinamidinium salts viz. 2-chloro-1,3-(bispiperidyl)trimethinium hexafluorophosphate which exists as form-I and form-II are also documented in the patent. Preparation process for etoricoxib by using such vinamidinium salts containing cyclic moieties is also described.
Nevertheless, there always exists a need to work out a newer synthetic approach that may lead to an improved and cost effective process for preparation of the said drug substance.